Big time drug dealers don't hoard cash anymore, they launder their money to make it legitimate and keep it in banks and investments. Small time drug dealers are poor and can't hoard cash.

Counter question to answer it,

What would they do with my hard earned money that's I my drawer when government replaces banknotes with new ones.

Its a process that slowly removes money from circulation. It's like swapping the water of a fish pond. You take some out, you add some back

Yeah they just change it out? I used to work cash in hand for a takeaway and I'd have to put hundreds into my account every few weeks.

Buy Bitcoin.